Modeling of Rotor Flux Barriers in a Brushless Doubly-Fed Reluctance Machine

A brushless doubly-fed reluctance machine requires partially-rated power converter, reduced maintenance, and operates without permanent magnets making it an attractive option for many applications such electrified propulsion and wind energy conversion system. However, BDFRMs have inherently poor torque density and high torque ripple. Since the flux modulation in a BDFRM is carried out by the rotor, the rotor structure plays an important role in torque production. This paper propose an analytical approach to model the effect of the rotor flux barriers on the mean and ripple torque. The method shows that the instantaneous torque is highly sensitive to the location of these flux-barriers. A rotor with two flux barriers per pole is used to illustrate the effectiveness of the proposed approach. Finally, the proposed modeling framework is used to optimize the rotor geometry to achieve a maximize mean torque with lower ripple. The estimated torque profile for the optimized rotor is verified using finite element analysis (FEA) of the machine.